Plant biomass solid fuel

ABSTRACT

A solid fuel is formed in a cuber to form body pieces formed of materials extruded through a die with a density greater than 35 lbs/cu ft; an energy content greater than 6500 BTU/lb; transverse dimensions less than 1.5 inches; and a length less than 4 inches; from plant biomass material which contains components when extended of greater than 1.0 inch. Primarily the materials are paper or other cellulose product and crop residue such as wheat straw. The cellulose and lignin from these materials act without additional binders as binders and encasing materials. The moisture content is maintained at a target value by mixing selected quantities of the materials without drying. The cubing machine has a feeding system where the space between the inner rotor and outer casing is smaller than 4 inches and the height of the outer flight is less than 1 inch.

The invention is related generally to the field of plant biomass solidfuel.

This application relates to and contains common subject matter with twoco-pending applications filed on the same date by the same applicantsunder Attorney Docket Nos. 85776-102 and 85776-202.

BACKGROUND OF THE INVENTION

Enormous quantities of agricultural residues or plant biomass materialsare produced as by-products of agricultural and commercial processing.Some of these products include Flax Shives which are currently beingused for bedding and for heating in large stoker boilers. Otheragricultural crop residues found in large quantities include; WheatStraw, Barley Straw, Corn Stover, Kentucky Blue Grass Screenings, Switchgrass and Bagasse. All of these can be collected and cubed to producesolid fuel.

The other product involved in this invention is paper residues collectedfrom recycling facilities. Due to the decrease in demand for recycledpaper products, more of these products are being disposed of in locallandfills. These paper products include OCC (Old Corrugated Cardboard),Mixed Waste, Boxboard and news print or any paper product that canshredded into a suitable size.

Currently coal is widely used as a fuel for many residential andcommercial combustion furnaces. Coal is widely available but isincreasing in cost and also contains many contaminants which render itless than entirely suitable as a fuel. However it's characteristics ofenergy contained, density, and remnant ash content are well establishedand suitable for combustion. Many such furnaces are therefore designedand produced particularly for the use of coal.

It would be highly desirable to provide a fuel product utilizing wastematerial such as plant residue, paper products and other materials wherethe products are formed into a structure which simulates coal in regardto its characteristics so that the fuel can be used as a simplereplacement for the existing coal fuel used in the existing furnaces.

There are many briquettes available for combustion in fireplaces andthese are commonly produced from compressed wood products such assawdust. However such briquettes are relatively expensive and do notprovide the characteristics of coal as a fuel. Yet further thebriquettes are expensive to produce since the materials from which theyare produced must be dried and the briquettes tend to producesignificant quantities of fines or dust when broken down. Thesecharacteristics reduce the desirability of such briquettes as areplacement for conventional coal in residential or commercial furnaces.

The technique for compression of materials to form a compressed ordensified product known as “cubing” is well established and widely used.The design of the Cuber has been available for 40 years and has changedlittle in that time. Such a Cuber is available from Cooper CubingSystems of Burley, Idaho USA. The Cuber of this type is robust andrelatively inexpensive. Such Cubers have however been used for thecompression of forage crops such as alfalfa. The alfalfa is introducedinto the cubing system and the high compression up to 6,000 psi of thematerial as it enters the series of dies creates an effective productwhich is extruded through the dies. The Cuber is particularly designedand arranged to provide and effective cubing action of the alfalfa tomaintain an attractive green appearance of the product so that it isattractive to the animals to be fed and to the handlers of thoseanimals.

Some attention has been given to the possibility for using such Cubersfor compressing other materials but little or no success has beenachieved to date.

An example of a Cuber of this type is shown in a brochure of the abovecompany and such Cubers include an exterior housing with a longitudinalaxis where the housing is held stationary with the axis horizontal. Afeed duct is provided at the top of the housing for feeding the materialto be cubed into the interior of the housing. The housing defines acylindrical inner surface at the feed section where a web of thematerial to be compressed enters through the feed opening.

At one end of the cylindrical feed section is provided a pair ofclamping disks with the disks lying in parallel radial planes of theaxis. One of the disks at the feed section has a central opening throughwhich the material feeds to be located between the two disks.

The disks act to clamp an array of radially extending, axially locateddies with the array surrounding the axis and located between theclamping disks. The clamping disks clamp the dies between them usingbolts passing through holes in the dies to squeeze the disks togetherand hold the dies at a fixed position surround the axis. The dies thusdefine a radially inwardly facing inlet mouth with a duct of the dieextending radially outwardly toward an outlet. Each die therefore formsan extrusion tube with the material being compressed into the inner endof the die.

Within the outer housing is provided an inner rotor with a generallycylindrical outer surface at the inner surface of the feed housing ofthe outer housing. The inner rotor also caries a press wheel lying inthe radial plane of the dies so that the press wheel rolls in the radialplane on the dies at the inlet mouth with the press wheel being mountedsuch so that as an axis of rotation of the press wheel rotates aroundthe axis of the outer housing. Thus as the press wheel rotates itsqueezes the material outwardly into the mouth of the die to becompressed and extruded through the die. The outer housing carries onits inner surface a plurality of upstanding flights extending from theouter surface inwardly toward the axis. The outer surface of the innerrotor also carries one or more flights which rotate with the rotor so asto sweep the material from the feed opening to the inlet of the dieswhere the material is engaged by the press wheel.

Outside the mouth of the dies where the material exits there is providedan angled plate so that the material as it exits engages the plate andis diverted to one side of its normal direction of movement thus causingbreakage of the extruded solid stream of the material into individualpieces giving the name “Cuber”, even though the length of the brokenpieces may vary and differ from the transverse dimension so that theproduct produced is not literally a “cube”.

SUMMARY OF THE INVENTION

It is one object of the present invention to provide a solid fuel formedfrom a plant biomass material.

According to the first aspect of the invention, there is provided asolid fuel material for combustion comprising:

a series of body pieces each formed of compressed materials extrudedthrough a die such that each body piece has a peripheral, longitudinallyextending, outer surface with each body piece being severed from nextadjacent body pieces to form two surfaces transverse to the peripheralsurface;

each body piece having a density greater than 35 lbs/cu ft;

each body piece having an energy content greater than 6500 BTU/lb;

each body piece having dimensions in the transverse direction which areall less than 1.5 inches;

substantially all the body pieces having a length in the longitudinaldirection between the transverse surfaces which is less than 4 inches;

wherein the compressed materials comprise plant biomass materials;

wherein the plant biomass material contains at least some componentswhich have a dimension when extended of greater than 1.0 inch.

Preferably the plant biomass material comprises a quantity of cellulosesufficient under heat and pressure to effect binding of the materialswithin the body pieces.

Preferably the plant biomass material comprises a quantity of ligninsufficient to generate an exterior casing around the peripheral surfaceof polymerized lignin.

Preferably the body pieces each have a casing around the peripheralsurface of polymerized lignin which is arranged to apply containingforces to an interior of the body pieces.

Preferably the compressed materials consist essentially of the plantbiomass materials, so that there are no additional materials such asadditional binding materials.

Preferably each body piece has dimensions in the transverse directionwhich are less than 1.0 inches. This may be a square in cross sectionbut alternatively circular or other cross sections may be formed throughthe extrusion die.

Preferably substantially all of the body pieces have a length less than2 inches. This length and transverse dimension allows flowcharacteristics similar to that of coal and allows passage of thematerial through a 5 inch diameter auger without blockages.

Preferably the density lies in the range about 35 to about 55 lbs/cu ft.

Preferably the thermal energy lies in the range about 6500 to about 8500BTU/lb.

Preferably the body pieces consist essentially of plant biomass materialselected as an admixture arranged to provide a quantity of cellulosesufficient to effect binding under heat and pressure of the materialswithin the body pieces and to include a quantity of lignin sufficient togenerate an exterior casing formed from polymerized lignin. The amountsmay be at least 10%, and more preferably 15 to 25%, by weight ofcellulose; and 0.5% to 5% by weight of lignin.

Preferably the body pieces have a moisture content of 5 to 8%.

Preferably the compressed materials produce a quantity of ash aftercomplete combustion of less than 10% and a quantity of ash aftercomplete combustion which contains less than 20% of Calcium, 20% ofpotassium and 75% silicon.

Preferably the plant biomass material is shredded such that it containsat least some components which have a dimension when extended of greaterthan 4.0 inches and contains comminuted components where the proportionof components having a dimension when extended of less 0.5 inches isless than 40%.

Preferably the compressed materials consist essentially of plane residuein the range 90% to 50% and a material forming a refined cellulose inthe range 50% TO 10%.

The plant residue may be wheat or barley straw, flax shives, corn stoveretc.

The refined cellulose may be formed from steam exploded wheat and/orbarley straw or paper.

General Description

The arrangement described herein provides a method of producing a solidfuel cube capable of being used in various heating systems. The fuel iscomprised of both agricultural crop residues and paper products.

More specifically the invention involves cubing biomass material in amixture that will enhance cube durability and energy content. Inparticular the invention concerns the use of agricultural crop residuesand paper products blended accordingly to produce a high quality solidfuel.

Described herein is a method of biomass fuel production using a modifiedcubing system. The invention involves cubing biomass material from amixture that forms a briquette having enhanced cube durability andenergy content. In particular the invention concerns the use ofagricultural crop residues and paper products blended accordingly toproduce a high quality solid fuel.

Specifically, material is selected that has high levels of cellulose andlignin which will aid in binding the products together. As discussedbelow, in preferred embodiments, the briquettes have at least 10% andpreferably approximately 15%-26% cellulose content and 0.5%-5% lignin.It is of note that starches found in some residues will also aid inbinding and elevate the energy content. It is noted that corn residuesfor example corn stovers are a suitable source of starches.

As discussed below, agricultural crop residues and paper products aremixed as discussed below, densified in a cubing device and then cooled.

Examples of agricultural crop residues include but are by no meanslimited to flax shives, wheat straw, barley straw, corn stovers,Kentucky blue grass screenings, switch grass and bagasse.

Flax shives are the by-product that is left over from the mechanicalextraction of the fiber component of the flax straw. Depending on theequipment used to decorticate the straw some fiber will be passed withthe shives. Shives would include any materials from the plant discardedafter fiber extraction.

Corn stovers or corn residue is the plant matter left over after combineharvesting. When the grain is harvested by means of a combine with acorn header, the residues including the cob and the leaf matter wouldall be included in the term corn stovers.

Hemp herd is the by-product that is left over from the mechanicalextraction of the fiber component of hemp. Depending on the equipmentused to decorticate the hemp, some fiber will be passed with the herd.Hemp herd would include any materials from the plant discarded afterfiber extraction.

Bagasse consists of any plant matter left over from the sugar extractionprocess of a sugar cane plant. This would also include all residues leftover in the field after harvest.

The paper products may be paper residues collected from recyclingfacilities. Suitable paper products may include but are by no meanslimited to the following: OCC (old corrugated cardboard), mixed waste,boxboard and news print or any paper product that can shredded into asuitable size to be mixed with the agricultural crop residues, asdiscussed below.

As discussed herein, in a preferred embodiment, the raw materials areshredded so to be no larger than 3 inch, so that the metering anddelivery systems to the cubing device will not plug during the process.It is noted that typically larger pieces are less desirable as thesewill affect the durability and density of the finished product.Specifically, the larger pieces will tend to break out of the briquettesor cubes, thereby generating a lot of fines. As used herein, 3 inchrefers to the diameter in the case of paper products and length forstraws or crop residues when the materials are expanded from theircrushed condition in the finished extruded product.

In some embodiments, wood particles can be added to the mixture, asdiscussed below. As will be appreciated by one of skill in the art, thesmaller the wood particles are, the better their binding characteristicsbecome. In other words, the more the wood particles are blended into themixture that forms the briquettes, the more durable and dense thefinished briquette product becomes.

As will be appreciated by one of skill in the art, wood from any kind ofwood product may be used, for example but by no means limited to DouglasFur, Pine, Spruce and Poplar.

The wood increases overall energy content of the final product,decreases overall ash content and helps with binding and durability ofthe briquettes.

As discussed below in the examples, the agricultural crop residues, thepaper products, lime and in some embodiments wood products are mixedtogether at a moisture content between 10 to 25%. If the moisture fallsbelow 10%, addition of water is required. In some embodiments, theaddition of water is done via small jets that are located in themetering bin. Preferably, fine water droplets are used as the goal is toachieve the fastest absorption rate as possible so the moisture will beconsistent in the mixture. The limiting factor on the nozzle size is thepurity of the water and system pressure. The moisture is arranged asexplained hereinafter so as not to exceed 25%.

Following mixing, unit portions of the mixture are densified into abriquette, where the very high levels of compression generally greaterthan 6000 psi will generate heat so that the dies can be heated to inexcess of 250° F., which will cause some of the lignin components in themixture to break down further and subsequently produce a very hardexternal shell and a durable product.

There is generally at least one second dwell time in the dies. Dwelltime is the time that the materials enter the dies to the time where thematerials exit. The dwell time is dependant on temperature. The longerthe material under compression is exposed to an elevated temperature themore the materials will bind together. The material preferably dwells inthe dies for at least 1 second in order for the binding agents toactivate or a poor quality product may result.

The densified briquettes are then cooled to room temperature. In apreferred embodiment, the briquettes are passed to a cooler. The coolerhas a large perforated floor which the freshly made briquettes travelon. As the briquettes travel on the floor by a large drag chain, largefans circulate air though them. It takes approximately 20 minutes tocool the cubes to ambient temperature. Fines are removed by theperforations in the floor and are carried out by the return of the dragchain and recycled.

It is of note that in these embodiments, the cubes are actively cooledto room temperature. If the cubes where piled and left to air dry, theslow cooling can deteriorate the cubes to the point where they fallapart into fines. The active cooling is therefore desirable to set themany binding agents within the mixture so that a high quality product isformed.

The target is to achieve an energy value above 6500 BTU/lb andpreferably in the range about 6500 to about 8500 BTU/lb. The average BTUof the mixtures listed below is 7900 BTU per pound @ 7% moisturecontent.

As will be apparent to one of skill in the art, the agricultural cropresidues, paper products and wood particles may be prepared for cubingby means known in the art, for example but by no means limited to tubgrinders, hammer mills and the like. Preparation of products for use areas follows: agricultural crop residues need to be shredded into suitablesize in order to be properly distributed in the mixture. The optimumsize is 3 inches or less. Paper products need to be shredded intosuitable size in order to be properly distributed in the mixture. Theoptimum size is 3 inches or less. Wood residues need to be processedinto suitable size in order to be properly distributed in the mixture.The optimum particle size is 1 inch or less.

As discussed herein, all products and additives are mixed together asper specified mixtures by means of a mixing unit and/or a meteringsystem or the like. The mixture is to be homogenous and between 10% to25% moisture, as discussed above.

As discussed above, the mixture is then densified by means of a cuberwith the operating temperature is to be 140 to 250 Fahrenheit to achieveproper bonding of these mixtures. Dwell time in die should be regulatedto a minimum of 1 second as discussed above.

The following are typical examples of materials which can be used:

EXAMPLE I

Flax Shives 90% to 50%

Shredded paper (particle size to be less than 3 inch) 10% to 50%

EXAMPLE II

Flax Shives 90% to 50%

Shredded paper (particle size to be less than 3 inch) 10% to 50%

Shredded wood and/or sawdust 10% to 50%

EXAMPLE III

Kentucky Blue Grass screenings 90% to 50%

Shredded paper (particle size to be less than 3 inch) 10% to 50%

Shredded wood and/or sawdust 10% to 50%

EXAMPLE IV

Shredded wheat straw and/or barley straw 90% to 50%

Shredded paper (particle size to be less than 3 inch) 10% to 50%

Shredded wood and/or sawdust 10% to 50%

EXAMPLE V

Shredded corn stover 90% to 50%

Shredded paper (particle size to be less than 3 inch) 10% to 50%

Shredded wood and/or sawdust 10% to 50%

EXAMPLE VI

Shredded sugar cane (Bagasse) 90% to 50%

Shredded paper (particle size to be less than 3 inch) 10% to 50%

Shredded wood and/or sawdust 10% to 50%

In all cases the moisture content is to be within 10% to 25%

BRIEF DESCRIPTION OF THE DRAWINGS

One embodiment of the invention will now be described in conjunctionwith the accompanying drawings in which:

FIG. 1 is an isometric view of a cubed solid fuel product according tothe present invention.

FIG. 2 is a schematic isometric view of plant for manufacture of thefuel product of FIG. 1.

FIG. 3 is an exploded view of one cuber of the plant of FIG. 2.

FIG. 4 is an isometric view of the cuber of FIG. 3.

FIG. 5 is a longitudinal cross sectional view of the cuber of FIG. 3.

FIG. 6 is a longitudinal cross sectional view of the inner rotor and theouter housing at the feed section only of the cuber of FIG. 3.

FIG. 7 is an isometric view of the inner rotor and the outer housing atthe feed section only of the cuber of FIG. 3.

In the drawings like characters of reference indicate correspondingparts in the different figures.

DETAILED DESCRIPTION OF THE EMBODIMENTS AS SHOWN

In FIG. 1 is shown one piece formed by the cubing system describedherein after. This single piece is indicated at 10 and forms one of amultitude of such pieces which are extruded and then broken to length asdescribed herein after.

Each piece 10 is extruded in square cross section to form top and bottomsurfaces 11 and 12 and side surfaces 13 and 14. These surfaces are flatand are formed from the inside surface of the die as described hereinafter.

The piece so formed is formed from the plant biomass material previouslydescribed where the high temperatures generated in the compressionprocess of the Cuber acts to cause the cellulose in the material to actas a binder within a central area 15 of the piece. Lignin within thematerial is driven to the exterior and is polymerized by the hightemperature action to form a hard outer casing 16.

The high compression of the cubing system described herein afterprovides a densification of the materials to provide a density of thefinished piece which is greater than 35 lbs/foot³ and preferably in therange from 35 to about 55 lbs/foot³. The die is selected so that thetransverse dimensions of each side as indicated at D are less than 1.5inch and more preferably less that 1.0 inch. The cubing system isarranged so that the length of the product as indicated at L between thetwo broken ends is preferably of the order of 1-2 inch and substantiallyall of the pieces have a length of less than 2 inch. This length can beselected as described herein after by adjusting the system so that thebreakages occur after extrusion of a length of material to provide thelength of the piece as required.

In some cases some of the pieces may have a length up to 4 inch. Howeverin order to simulate the flow characteristics of coal, it is highlydesirable that the length of the pieces is less than 4 inch and morepreferably less than 2 inch.

The dimensions as described above allow the product to simulate the flowcharacteristics of coal both in passage through openings and also intransport of the material through augers and particularly theconventional or common 5 inch auger which is used in many furnaceconstructions.

As described herein after, the plant materials are selected such thatthey are shredded to a length of the pieces when extended which isgreater than 1 inch. Thus the pieces when compressed may crumple intosmall elements or maybe laid into the structure as pieces as indicatedat 20 where the pieces are laid through the structure and providecontinuous connection through the structure. This selection of ashredding action which provides materials having a length greater that 1inch and commonly greater than 2 inch or 4 inch reduces the amount ofdust or fines within the structure so that the pieces when they breakduring the forming action or at any later time do not crumble to dustbut instead break along fault lines generated by the elongate piecessuch as the piece 20 first to break into larger chunks rather than meredust or fines.

The selection of the materials as described herein provides a level ofcellulose in the mixed materials which is sufficient to cause a bindingaction within the structure of the piece 10. Thus the level of celluloseis preferably greater than 10%. The cellulose acts as a binding agentduring the heating of the material during the extrusion process.

In addition the selection of the materials is arranged to provide alevel of lignin which is in the range 0.5 to 5% and is sufficient togenerate a polymerized layer of the lignin on the outside surfaceforming a hard shiny shell of the casing as indicated at 16. This hardshiny shell of the lignin acts to conation the remaining materials onthe interior to reduce again breakdown of the product and release of anyfines or dust.

The materials as described herein are selected to provide under theamount of compression as described to provide the density as described athermal energy in the range of about 6500 to about 8500 btu/lb. Thisagain simulates the characteristics of coal which typically has anenergy content in the range 7000-8000 btu/lb.

The compressed materials as described herein are selected to provide aquantity of ash after complete combustion of the product which is lessthan 10%. In addition the materials are selected so that the ash aftercomplete combustion contains less than 20% of calcium, 20% of potassiumand 75% of silica. Again this selection of the materials as describedabove provides such an ash content to again simulate the characteristicsof coal so that the combustion does not provide excessive amounts of ashwhich would otherwise interfere with the use of existing coal firedfurnace systems.

The shredding action as described above is carried out so that theamount of small components or comminuted components within thestructures is maintained relatively low. Thus the proportion ofcomponents having a dimension of less than 0.5 inch is less than 40%.

Turning now to FIG. 2 there is shown schematically a layout of aconstruction of a plant for manufacturing the fuel product of FIG. 1.The plant comprises a shredding system generally indicated at 21 intowhich the selected products for manufacturing the fuel are introducedfrom a supply 22. The shredder system as shown is adjustable so that itcan be adjusted to the characteristics of the incoming materials.Alternatively separate shredders may be provided for differentmaterials. When shredded the materials are supplied into a plurality ofseparate supply containers 23 and 24. These contain blending rollers andmetering rollers so that the material supplied to these containers canbe blended to a homogenous mixture and can be discharged through ametering system into a conveyer 25. The rate of supply from thecontainers 23 and 24 can be adjusted so as to provide predeterminedquantities of the materials from those two containers into the conveyer25. Thus the mixture may be modified to different ratios as determinedby the adjustment of the system under control of a suitable computercontrol system (not shown). The conveyor 25 transfers to an elevatingconveyor 26 which supplies to a metering system 27. The metering system27 acts as a surge tank to maintain a continuous supply from a dischargeat the base 27 a of the metering system 27. Thus the conveyor 25 isoperated periodically to maintain the surge tank 27 at a required fillcondition between upper and lower limits.

The surge tank or metering unit 27 supplies three separate cubers 28, 29and 30 as described in more detail herein after. Thus in the embodimentshown the metering system 27 separates the supplied mixture into threeseparate transferred ducts 28 a, 29 a and 30 a supplying the threeseparate cubers with the material at the required predetermined rate.

The output from the cubers which is defined by the multitude ofindividual pieces of the type shown in FIG. 1 is deposited to a conveyor31 which transfers the cubed material into a cooler 32. From the coolerthe material is discharged into an elevator 33 and stored in productsupply tanks 34 and 35 for discharge into transportation trucks 36 fortransportation to a distribution network.

The cooler 32 is in effect an ambient air cooling system which depositsthe materials from the conveyor 31 in a mat over a perforated floor ofthe cooler so that the air drawn through the material from theperforated floor by a fan acts to apply cooling air onto the product toreduce its temperature from an elevated temperature emerging from theextrusion dies to an ambient temperature. Thus the temperature as thematerial enters from the extrusion process can be of the order of1702200 degrees F. and is cooled in the cooler down to a temperature ofthe order of ambient temperature of approximately 70 degrees.

This cooling action ensures that the binding material provided primarilyby the cellulose is reduced in temperature to a set temperature thusmaintaining the pieces in integral condition and reducing thepossibility that the materials will break down to smaller pieces thanthe desired cubes of the above described dimensions.

The cooler carries the mat of the material along the length of thecontainer forming the cooler using a large drag chain or conveyorarrangement which transports the pieces across the horizontal floor froman inlet end toward a discharge end. During this movement the materialsare deposited onto the perforated floor so that any extra fines breakingaway from the pieces can collect through the floor into a suitablecollection system where they can be returned into the chambers 23 and 24for repeated processing.

One of the cubing machines is shown is FIGS. 3, 4 and 6. This comprisesan outer housing 40 in the form of a cylindrical drum 41 with an inletduct 39 supplying the feed material from the conveyor into the interiorof the drum. The drum has a cylindrical inside surface 42. At the end ofthe drum is provided a first clamping disk 43 which is welded to the endof the tube forming the drum and extends outwardly there from to form anannular disk shape as indicated at 44. The disk has a circular interior45 matching the end of the drum 41. Thus material passing along theinside surface of the drum can pass through the hole 45 in the disk andenter the area on the outside face of the disk 43 and adjacent to thesecond end disk 46. The disks lay in common radial planes of an axis 47of the drum. The disks are generally coextensive. The disks act asclamping disks and have a series of mounting holes 48 in cooperatingpatterns for receiving axially extending bolts between the disks. Thedisks thus can be used to clamp a series of dies 50 so that the dies arearranged angularly around the axis 47 with each die providing a ductthrough which the material from the interior of the drum can beextruded. The dies thus are arranged around the axis with an inside faceof the die facing toward the interior and located just outside the inneredge 45 of the disk 43. Each die thus forms a tube extending radiallyoutwardly from the inner end at the edge 45 to an outer end extendedbeyond the outer edge of the disk.

The inner rotor 55 mounted within the outer housing 40 comprises a shaft56 extending along the axis 47. The shaft 47 is mounted in end bearingswith one bearing be located in an end capped 57 of the disk 46 and thesecond bearing being located in the end plate 53. Thus the shaft iscarried on the axis 47 and can rotate around the axis 47 driven by amotor 58.

The inner rotor 55 carries a feed drum 59 which is located axiallyaligned with the inside surface of the casing 41 so that the feed drumacts to carry the feed material along the inside surface of the casing41 to the circular opening 45 in the disk 43 so that the material can bepresented through that opening to the dies.

The inner rotor 55 further includes a press wheel 60 carried on asupport 61. The press wheel 60 is mounted with a wheel axis 63 offsetfrom the shaft 56 and the axis 47. Thus the axis of the press wheel canbe rotated around the axis 47 so that the wheel rolls around the insidesurfaces of the dies moving from each die to the next as the shaftrotates. Support 61 is suitably designed to carry the press wheel toapply onto the inside surfaces of the dies a significant force providingcompression of the material within the dies up to a force preferablygreater than 6000 psi and preferably up to a pressure of the order of10000 psi.

The drum 59 has an outer surface 63 which is located at a positionspaced from the inside surface 42 of the outer casing 41. This definestherefore an annular chamber between these two surfaces. On the outsidesurface of the drum 59 is provided a flight 64 which extends diagonallyalong the outside surface 63 so as to form a helix defining an augerwhich rotates around the axis 47 and thus acts to carry material axiallyalong the outside surface 63 of the drum toward the end 66 of the drumat the press wheel 60. It will be appreciated that the end 66 is locatedat the opening 45 in the disk 43 so that the action of the flight 64 isto carry the material into the area between the two disks and throughthe opening 45 to feed into the compression zone defined between theinside surfaces of the dies and the press wheel.

On the inside surface 42 of the drum 41 is provided a series of flights70, 71, 72, 73 and 74. These flights have a leading end on the interiorsurface 42 at the feed opening 39. Thus the leading ends are spacedaxially along the inside surface equal-distantly so as to receive equalamounts of the mat of material which is fed through the opening 39. Eachflight curves around the surface 42 so that the flight moves axiallyalong the inside surface 42 and curves around the inside surface 42 sothat the space between the flights for receiving the material graduallyturns from its initial axial position around to form a space between theflights at the opening 45 in the disk 43. This space gradually increasesin width since the distance axially at the feed opening is less that thecircumference of the opening 45.

The flight 64 thus cooperates with the flights 70 through 74 to sweepthe material from the feed opening in a smooth flow to be dischargedaxially through the opening 45 in the disk 43.

It is essential that the feed movement is smooth so that the material isreleased through the opening 45 as a smooth flow to enter thecompression space. Any changes in the thickness of the material as itemerges leads to vibration in the system since the amount of material tobe compressed varies around the dies. Such variation is unacceptable inthe operation of the device and therefore a smooth flow of the materialin a mat form at the feed opening through the system to the dischargeinto the compression zone is essential for the operation of the device.

The smooth flow of the materials described herein is obtained byproviding a spacing between the outside surface 59 and the insidesurface 42 which is less than 4 inch and is preferably less than 3 inchand more preferably of the order of 2.5 inch.

In addition the height of the flights 64 relative to the flights 70through 74 is arranged so that the flights attach to the outer surface42 which project inwardly toward the axis are greater in height than theflight 64. In practice with a spacing between the surfaces 42 and 63 ofthe order of 2.5 inch, the flight 64 has a height of the order of 1.0inch and the flights 70 through 74 have a height of the order of 1.5inch. Thus the ration of these heights is preferably greater than1.3:1.0 and more preferably greater than 1.5:1.0.

This relatively small spacing between the surfaces 42 and 63 togetherwith the change in ration of the heights of the flights has been foundto provide an effective feeding action of the materials with which thepresent invention is concerned. The feeding action is maintained smoothso that a constant supply of the feed material enters the compressionzone between the press wheel and the dies to ensure a constant feed ofthe material through the individual dies as a solid material extrusion.

The dies 50 are held in place in an annular array surrounding thecompression zone with each die extending radially outwardly from theaxis 47. In practice the dies are formed in two halves so that each diepiece has on each side one half of the tubular opening forming the die.Thus when the pieces are clamped together the two halves of the ductforming the die are closed.

In the event that a foreign object enters the feed system and is notpreviously extracted by the feed preparation process, that foreignobject may enter the compression zone and when located between a diepiece and the press wheel may be of a nature that it cannot becompressed into the die opening. Such foreign objects can be stones orrocks, metal pieces or other solid objects. The preparation system canuse conventional processes for extracting such materials such asmagnets, gratings and the like. However it is generally impossible toextract all such materials and therefore the machine utilizes shearbolts for mounting the dies in place so that the presence of such aforeign object acts to expel one or more of the die pieces radiallyoutwardly by shearing the mounting bolts for that or those die pieces.

In order to obtain an immediate indication of the movement of a diepiece radially outwardly due to the presence of a foreign object, a tape98 (FIG. 5) is mounted around the die pieces on one side of the dieopenings at the outlet with the tape including one or more peripherallyextending conductors 99. On outward radial movement of a die piece,therefore, the tape 98 is fractured thus breaking one or more conductors99. This break in a conductive path can be sensed by detecting a changein voltage or a change in current flow and can be communicated to thecentral control system for the plant of FIG. 2. The central controlsystem can therefore shut down immediately the rotation of theparticular cubing machine where the detection has occurred to preventfurther damage.

Turning now again to FIG. 2, the process of mixing the materials toprovide the feed to the individual feeders is now described in moredetail. In particular the feed materials are selected into one or otherof the supply containers 23 or 24 depending primarily on the moisturecontent. Thus in the container 23 is provided materials which aregenerally of a drier nature such as recycled paper products. Thismaterial acts as a dry component for the mixture and allows a secondcontainer 24 to receive materials of differing levels of moisturecontent.

Target moisture content for the materials supplied to the cubers is ofthe order of 17%. However for operation to occur, the moisture contentcan lie in the range 10% to 25%.

The materials selected for the container 23 are preferably arranged toprovide a moisture content of the order of 6% to 8%. This is typicalfrom recycled paper products whether those products be newsprint fromrecycled newspapers or commercial products such as recycled cardboardmaterials. These materials are therefore shredded and entered into thesupply container 23 to provide a supply of the low moisture materialsfor admixture into the total content at the conveyor 25.

Other refined cellulose materials may also be used instead of or as anaddition to paper products conveniently used. Paper products are widelyavailable at low cost as a recycled material. However as an alternativeother materials can be used for example steam exploded straw can be usedwhich is a significant source of refined cellulose material provided ina form which presents the cellulose in a manner which allows it to beutilized in the binding process as a binding material when activated bythe heat and steam generated by the compression in the die as previouslydescribed.

Steam exploded straw is generated in a process by which a quantity ofstraw is heated in moisture to a temperature significantly greater than100 degrees C. by applying pressure to the contents. Thus super heatedsteam enters the cellulose structure of the straw and on instantaneousrelease of the pressure the presence of the super heated steam withinthe cellular structure act to explode the cellular structure to formrefined cellulose in a fluffy low moisture content condition. Theprocess can be managed so that the material when release from theprocess has the required moisture content of 6-8% which is suitable forthe low moisture materials within the container 23.

The steam exploded straw also releases the lignin content which can beextracted using solvents if required or can remain within the structureas part of the binding process to generate the outer shell as previouslydescribed.

The second container 24 is used to contain the variable feed materialwhich can vary in moisture content since its origin may varysignificantly. Even straw within a storage pile of cylindrically balescan have significantly different moisture content throughout the piledbales. Typically the materials to be supplied to the container 24 willhave a moisture content significantly greater than the target moisturecontent of 17%. Moisture contents of up to 60% are possible.

The two materials supplied therefore to the containers 23 and 24 areshredded and supplied at the moisture content that they contain as theyare received from whatever origin of the material arises. The moisturecontent is measured using probes 23 a and 24 a so that the moisturecontent of the material as it reaches the conveyer 25 is accuratelydetermined. The control system then acts to blend the materials onto theconveyor 25 in proportions with the intention of providing a mixedmaterial having a moisture content at the target value. As previouslystated the target value is typically of the order of 17% but can liewithin any value between 10% and 25% depending on process andconditions.

The moisture content of 17% is selected since it has been determinedthat the process tends to dry off during the cubing action approximately10% moisture by converting that moisture into steam which is thenreleased from the product after the cubing process. Thus an initial feedmoisture content of 17% is reduced by the release of 10% moisture to amoisture content of the order of 7% in the finished product as theyenter the cooling chamber 32.

The amounts of the materials from the dry container 23 and the wetcontainer 24 can therefore vary widely depending on the moisturecontent. In addition to the moisture value it is necessary to insurethat the finished material contains at least 10% cellulose and at 0.5 to5% lignin. Thus the material cannot consist solely of the paper sincethis has little or no lignin content. Therefore is a minimum quantity ofthe straw or other crop residue material which is required in themixture and this also must be taken into account in the moisture mixingprocess.

However, the mixing process is arranged to provide the target value ofthe order of 17% without the application of any heat. In the event thatthe target value cannot be maintained at the 17% level this can beallowed to increase up to 25% and the process still operateseffectively.

In the event that the moisture content drops below 17%, additionalmoisture can be added at the surge tank 27 in the form of spray nozzleslocated in that tank. However this is only carried out when it isessential to do so. Thus the intention is that the materials be managedso that wherever possible the moisture content is maintained above the10% value and preferably at the 17% value simply by managing the mixingprocess. In order to carry out this mixing action to the required levelsof cellulose, lignin and moisture, additional containers may be providedso that the management of the system can utilize different strawproducts at different moisture contents within different supplycontainers. Another supply container might be used for wood productssuch as saw dust when available. In this way more flexibility of mixingis available to allow the control system to maintain better the accuracyof the moisture content while providing the minimum values andpreferably significantly higher values of the cellulose and lignincontent.

In the event that the moisture content exceeds the target value of 17%and reaches up to the maximum value of 25%, this moisture content can beprocessed through the system. However the moisture content of theproducts entering the chamber 32 are measured by a sensor 32 a. Thetarget value of the moisture content of the finished product is 6-8% inthe event that the moisture content of the feed material is 25% to beappreciated that the moisture content of the product at the sensor 32 awill be of the order of 15%. In the event that such a moisture contentabove the target moisture content is detected, the cooling process inthe chamber 32 is slowed in order to increase the dwell time of thematerials within the cooler chamber 32. Thus the product is reduced inmoisture content by being maintained within the cooling chamber 32 for alonger period of time to reduce or extract the moisture which is drawnfrom the product by the air flow. This drying action is effected withoutthe application of additional heat and is carried out strictly by theambient air flow which carries the heat and reduces the temperature tothe ambient value of the order of 17%.

The whole process therefore is carried out by effectively managing themoisture by the mixing action and by the cooling action without therequirement for added heat at any point in the process. It would beappreciated of course that adding heat is a significant expense in themanufacture of the product so that the economics of the process may becancelled if significant quantities of drying heat are required. It isappreciated in this regard that the product is competing with coal whichrequires as a cost input only the cost of extraction and transportationwithout any product cost and generally without any drying cost. It isessential therefore in the present process that the amount of heatrequired be maintained at a minimum so as to maintain the economics ofmanufacture of the product as close to that of the coal materials ofwhich the present materials are in competition.

The supply materials are therefore typically wheat and/or barley strawwhich provide the available lignin together with the paper materials orother refined cellulose which provides the available cellulose and thelow moisture content for mixture with the generally higher moisturecontent of the crop residue. In place of the wheat or barley straw,other crop residues can be used such as flax shives, corn stover. Othercrop residues such as canola straw can also be used. The use of thelignin and the cellulose as the binding and encasing elements avoids thenecessity for the addition of other binding materials of a nature whichdo not contribute to the combustion product and require additionalcosts.

While the preferred embodiments of the invention have been describedabove, it will be recognized and understood that various modificationsmay be made therein, and the appended claims are intended to cover allsuch modifications which may fall within the spirit and scope of theinvention.

1. A solid fuel material for combustion comprising: a series of bodypieces each formed of compressed materials extruded through a die suchthat each body piece has a peripheral, longitudinally extending, outersurface with each body piece being severed from next adjacent bodypieces to form two surfaces transverse to the peripheral surface; eachbody piece having a density greater than 35 lbs/cu ft; each body piecehaving an energy content greater than 6500 BTU/lb; each body piecehaving dimensions in the transverse direction which are all less than1.5 inches; substantially all the body pieces having a length in thelongitudinal direction between the transverse surfaces which is lessthan 4 inches; wherein the compressed materials comprise plant biomassmaterials; wherein the plant biomass material contains at least somecomponents which have a dimension when extended of greater than 1.0inch.
 2. The fuel material according to claim 1 wherein the plantbiomass material comprises a quantity of cellulose sufficient under heatand pressure to effect binding of the materials within the body pieces.3. The fuel material according to claim 1 wherein the plant biomassmaterial comprises a quantity of lignin sufficient to generate anexterior casing around the peripheral surface of polymerized lignin. 4.The fuel material according to claim 1 wherein body pieces each have acasing around the peripheral surface of polymerized lignin.
 5. The fuelmaterial according to claim 3 wherein the casing is arranged to applycontaining forces to an interior of the body pieces.
 6. The fuelmaterial according to claim 1 wherein the compressed materials consistessentially of the plant biomass materials.
 7. The fuel materialaccording to claim 1 wherein each body piece has dimensions in thetransverse direction which are less than 1.0 inches.
 8. The fuelmaterial according to claim 1 wherein each body piece is square intransverse cross section with a width of less than 1.0 inch.
 9. The fuelmaterial according to claim 1 wherein substantially all of the bodypieces have a length less than 2 inches.
 10. The fuel material accordingto claim 1 wherein the density lies in the range about 35 to about 55lbs/cu ft.
 11. The fuel material according to claim 1 wherein thethermal energy lies in the range about 6500 to about 8500 BTU/lb. 12.The fuel material according to claim 1 wherein the body pieces consistessentially of plant biomass material selected as an admixture arrangedto provide a quantity of cellulose sufficient to effect binding underheat and pressure of the materials within the body pieces and to includea quantity of lignin sufficient to generate an exterior casing formedfrom polymerized lignin.
 13. The fuel material according to claim 1wherein the compressed materials contain at least 10% by weight ofcellulose.
 14. The fuel material according to claim 1 wherein thecompressed materials contain 0.5 to 5% by weight of lignin.
 15. The fuelmaterial according to claim 1 wherein the body pieces contain bindingagents provided essentially by the admixture of plant biomass material.16. The fuel material according to claim 1 wherein the body pieces havea moisture content of 5 to 8%.
 17. The fuel material according to claim1 wherein the compressed materials produce a quantity of ash aftercomplete combustion of less than 10%.
 18. The fuel material according toclaim 1 wherein the compressed materials produce a quantity of ash aftercomplete combustion which contains less than 20% of Calcium, 20% ofpotassium and 75% silica.
 19. The fuel material according to claim 1wherein the plant biomass material contains at least some componentswhich have a dimension when extended of greater than 4.0 inches.
 20. Thefuel material according to claim 1 wherein the plant biomass materialcontains comminuted components where the proportion of components havinga dimension when extended of less 0.5 inches is less than 40%.
 21. Thefuel material according to claim 1 wherein the compressed materialsconsist essentially of wheat and/or barley straw and a material forminga refined cellulose.
 22. The fuel material according to claim 1 whereinthe compressed materials consist essentially of wheat and/or barleystraw in the range 90% TO 50% and a material forming a refined cellulosein the range 50% TO 10%.
 23. The fuel material according to claim 1wherein the compressed materials consist essentially of flax shives anda material forming a refined cellulose.
 24. The fuel material accordingto claim 1 wherein the compressed materials consist essentially of cornstover and a material forming a refined cellulose.
 25. The fuel materialaccording to claim 1 wherein the compressed materials consistessentially of crop residue and a material forming a refined cellulose.26. The fuel material according to claim 1 wherein the compressedmaterials consist essentially of crop residue, wood and a materialforming a refined cellulose.
 27. The fuel material according to claim 1which has combustion emissions containing less than 1% sulphur andsubstantially no heavy metals.
 28. The fuel material according to claim1 which is shaped and arranged to pass through an auger having a flightdiameter of no greater than 5 inches.
 29. The fuel material according toclaim 21 wherein the material forming the refined cellulose is formedfrom steam exploded wheat and/or barley straw.
 30. The fuel materialaccording to claim 21 wherein the material forming the refined celluloseis paper.